The present invention focuses on charge control in an outdoor air treatment and ventilation system delivering properly conditioned outdoor air in HVAC systems. The primary benefit of using this type of system is the ability to properly heat, cool and/or dehumidify outdoor ventilation air independently of the other equipment in the system.
A problem occurs during the operation of a fresh air refrigeration unit having series connected condensers when a large part of the heat rejection of the refrigerant system takes place in the reheat coil. As more and more air is directed over the reheat coil, refrigerant temperature drops and refrigerant condenses. The cooler than normal refrigerant enters an outdoor condenser coil to be cooled even further. Since there is insufficient charge to support this operation, the condensation of refrigerant in the outdoor coil begins to starve the thermal expansion valve in the refrigeration system. In order to maximize the capacity of the reheat coil, the heat rejection in the outdoor condenser coil needs to be minimized and sufficient charge must be made available to the thermal expansion valve.